1. Field of the Invention
The present invention relates to a honeycomb structure, and a honeycomb catalyst body. More particularly, it relates to the honeycomb structure which is suitably used as a catalyst carrier to purify an exhaust gas, and the honeycomb catalyst body in which a catalyst is loaded on such a honeycomb structure.
2. Description of Related Art
An exhaust gas discharged from an internal combustion engine such as a car engine includes nitrogen oxides (NOx). From the viewpoints of influences on the global environment and the like, the purification of nitrogen oxides included in the exhaust gas is required. For example, a purifying method using an SCR catalyst is effective for the purification of the nitrogen oxides (NOx). Therefore, the SCR catalyst is broadly used in the purification of the exhaust gas discharged from the engine or the like (specifically, the purification of the nitrogen oxides included in the exhaust gas). The term “SCR” is an abbreviation off(“Selective Catalytic Reduction.” The term “SCR catalyst” means the catalyst which selectively reduces components to be purified by a reductive reaction. In particular, examples of the SCR catalyst can include a catalyst which selectively reduces the nitrogen oxides.
When the SCR catalyst is used to purify the exhaust gas, the SCR catalyst is loaded on a catalyst carrier, and used as a catalyst body sometimes. Examples of the catalyst carrier can include a honeycomb structure including partition walls to divide and form cells which become through channels of a fluid. The loading of the catalyst on the partition walls of such a honeycomb structure is referred to as catalyst coating sometimes.
As a gas treatment device including such a honeycomb catalyst body, for example, a gas treatment device including a flow channel material and a composite catalyst is suggested (e.g., see Patent Document 1). The flow channel material includes an inlet axial end, an outlet axial end, wall elements each having such a length as to extend from the inlet axial end to the outlet axial end, and a plurality of passages defined by the wall elements, surrounded in an axial direction and having opened ends. That is, the flow channel material becomes the above honeycomb structure. The composite catalyst includes particles having an average particle diameter in excess of about three microns, and has a washcoat state where the catalyst is substantially deposited on the wall elements. In the gas treatment device of Patent Document 1, an average roughness of the surface of each wall element does not substantially change from the roughness before the catalyst is loaded on the walls.    [Patent Document 1] JP 2010-516466 T
In an SCR catalyst to perform the purification of nitrogen oxides and the like, an amount of the SCR catalyst has a very large influence on a purification performance. Therefore, to enhance the purification performance by the SCR catalyst, a large amount of the catalyst is required. For example, in a honeycomb catalyst body in which the SCR catalyst is loaded on partition walls of a honeycomb structure, a large amount of catalyst coating is required. However, when the large amount of catalyst coating is performed, there occurs the problem that a pressure loss of the honeycomb catalyst body increases.
Moreover, in the honeycomb catalyst body in which the catalyst is loaded on the partition walls of the honeycomb structure, due to the thickness of a layer of the catalyst coating, the cell open frontal area decreases, and the open area ratio of the honeycomb structure decreases. Furthermore, there has been the problem that the increase of the pressure loss is incurred.
Furthermore, in Patent Document 1, a method of filling pores of the partition walls with the catalyst is disclosed. However, the method disclosed in Patent Document 1 has the problem that the pores of the partition walls cannot be filled with a sufficient amount of the catalyst.